1. Field of the Invention
The present invention relates to a disc cartridge in which a disc comprising information recording means is rotatably mounted and more particularly to a disc cartridge in which a portion at the vicinity of a hub disposed at the central portion of the disc is improved.
2. Description of the Related Art
As information processing apparatuses such as personal computers and personal word processors have been developed, magnetic floppy discs as handy information recording means as well as optical disc cartridges for optically reproducing information have been frequently used.
An external information recording device will now be explained by a 3.5 inch magnetic disc cartridge. The disc cartridge consists of a disc coated with a binder having powered magnetic material evenly distributed as a recording medium, and a case comprising a pair of integrally formed half cases made of ABS resin. In the center of the disc is a hub which has a central hole and a hole displaced from the center of the hub. In a corner of the case is a write protector for inhibiting information recording. In the case formed a pair of windows in which is inserted a magnetic head for reproducing information from a magnetic disc and recording the information on the magnetic disc. A movable U-shaped shutter made of metal covers a part of the case. A hole for the write protector is also formed in the case. In one of the half cases is formed a circular hole at which is exposed the hub provided in the central portion of the magnetic disc. On both surfaces of the case are attached liners made of non-woven fabric for removing foreign matter such as dust. Between one of the half cases and the respective liner is disposed a lifter for pressing the liner in a direction toward the magnetic disc. The U-shaped shutter is inserted in the case when both half cases are joined together. A spring engages the shutter so that the spring shutter covers the pair of windows formed in the case in the above-mentioned direction.
Ample space is left around the magnetic disc in the magnetic disc cartridge to allow the magnetic disc to be freely rotated. The magnetic disc is moved slightly in the case when the magnetic disc cartridge is swung by a external force or the like in an unused state in which the magnetic disc is not set on disc driving means. Since the magnetic disc is in contact with the liner by means of the lifter in this state, the lifter, magnetic disc and liners are sometimes rubbed with one another to produce dust which may cause trouble such as a reproducing error.
Recently, recording capacity has been increased not only in recording devices and recording material but also in the above-mentioned magnetic discs. The width of the tracks and the distance between the adjacent tracks have been rendered smaller and smaller, and a linear recording density per unit of the circumferential length on each track has been made higher and higher.
In doing so, there has been developed a magnetic disc coated with an alloy film such as Co-Cr by a vacuum process such as the sputtering method or the evaporating method, and a magnetic disc which has a supporter coated with magnetic powder such as Barium ferrite fine particles and a binder.
These magnetic discs having a high recording capacity has a narrower track width, a smaller distance between the adjacent tracks and a higher linear recording density than the conventional magnetic discs. Thus, dust has a large adverse effect on the magnetic disc. Specifically, dust of such a small size that does not cause trouble on the conventional magnetic disc having ordinary tracks and/or an ordinary line recording density is likely to bring about trouble on the magnetic disc having a large recording capacity. In other words, very fine dust causes drop-out. It is, therefore, necessary to reduce foreign matter such as dust produced in the magnetic disc cartridge.